I "need" a proportioning valve for dual m/c with drum brakes WTF??

So I want to do a dual m/c upgrade on my 60 Belair. I look in the Ecklers catalog and find a kit for the job. Here is what I found: http://www.lategreatchevy.com/chevy...er-with-four-wheel-drum-brakes-1955-1964.html

The kit comes with a proportioning valve. This doesn't make any sense to me. I know you need a proportioning valve for drum/disc setups but drum/drum?? Well, being the first to admit I don't know it all I drop a email to their tech line and this is the reaponse I get:

Hello,
The reason that you need the proportioning valve when working with a dual master cylinder arrangement is because the valve will provide a proper balance within the braking system to ensure that the system operates with the amount of braking in the front and rear. Even in a system that is all drum and non-power, the balance of pressure needs to maintained within the braking system. Thank you for your time and patience. Have a great day. If you have any further questions please feel free to contact us again so that we may****ist you in the future.

Ok now I'm really confused. My car (like most) has different size wheel cylinders front and rear. 1-3/16" front and 1" in the rear. Isn't this the way the pressure is balanced between the front and rear? There is no proportioning valve on the single pot m/c. It is my understanding the only difference between a single and dual m/c of the same bore is one chamber feeds the front and one feeds the rear.

Like I said in the beginning I don't know everything by a longshot but this just doesn't make sense to me. Please fell free to educate me. Thanks, Todd

 

You are correct that stock drum/drum systems don't need (or ever used, to my knowledge) a prop valve. By switching to a dual master with the same bore size as your single does not change the braking or balance, just splits the hydraulic system from one to two. The difference in wheel cylinder sizes, as you point out, creates the factory brake balance.

What you do need are residual valves with your vintage drum brakes, so check your dual master for them internally behind the tube seats, and add a 10 lb valve to each system if necessary.

And make sure that new master can attain FULL stroke before the pedal bottoms out or hits the floor.

 

Bob,

Thanks for the re-assurance. I am aware of the RPV's if they are not part of the m/c. One questuion on them though. Can they be mounted vertically? I know they are direction specific but not sure about the up and down. Todd

 

They can be mounted in any position as long as you have the direction of flow correct.

 

You're OK to mount them vertically, just keep them as close to the master as possible.

 

Sounds like a metering valave to me, puts the pressure to the front first so you don't lock up the rear and slide.
Doesn't matter if it is Drum/Drum or Disc/Drum or Disc/Disc, most of your stopping power will come out of the front brakes. The metering valve meteres more pressure to the front when you slam the pedal then balances the front and rear. It will also act as an isolator if you loose one side of the system.

 

Head up to Ellinton Ct to ECI, in person, and talk with someone real, and their business is brakes, not the whole car..

 

Nope ~ A Combination Valve (like they Show) is a Proportioning valve, Pressure Differential Valve and Metering Valve built into one unit. BUT it is NOT for Drum/Drum applications, it is for Disc/Drum and it does NOT put pressure to the fronts first. You know that the disc brake pad is normally in contact with the disc, while the drum brake shoes are normally pulled away from the drum. Because of this, the disc brakes are in a position to engage before the drum brakes when you push the brake pedal down.

The metering valve compensates for this, making the drum brakes engage just before the disc brakes. The metering valve does not allow any pressure to the disc brakes until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in.

Having the rear brakes engage before the front brakes provides a lot more stability during braking. Applying the rear brakes first helps keep the car in a straight line, much like the rudder helps a plane fly in straight line.

The pressure differential valve is the device that alerts you if you have a leak in one of your brake circuits. The valve contains a specially shaped piston in the middle of a cylinder. Each side of the piston is exposed to the pressure in one of the two brake circuits. As long as the pressure in both circuits is the same, the piston will stay centered in its cylinder. But if one side develops a leak, the pressure will drop in that circuit, forcing the piston off-center. This closes a switch, which turns on a light in the instrument panel of the car.

The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

As for that kit, a Proportioning valve wouldn't be a bad idea to make sure that the balance of the front to rear is correct, but a metering valve is not required (although I guess it wouldn't hurt anything).

 

Actually, a metering, or hold-off valve, does the exact oposite. It "holds off" front discs, and allows about 100 psi to rear drum brakes, so the shoes can overcome their return springs and contact the drums about the same time as the disc pads touch their rotors.
Where in the world did you learn about metering valves

 

any factory dual chamber m/c car w/ 4 wheel drums i've had has had a prop valve(all fomoco). i've used drum/drum prop valves with front discs and vice versa so i dont know if it matters-they all stopped fine.

 

I'm running a 5 port proportioning valve with a dual master on my 51' ,drums all around and it made a big difference by using it. my 2 cents!

 

Can you tell me one year/model Ford that ever used a prop valve with 4-wheel drums?

 

I have drums on all 4 wheels, dual MC with a balance bar, no proportioning valve. I have had it on the road for only a few weeks but is seems to stop on a dime.

 

2 i've had were a '66 fairlane and a '68 f-100

 

My car (like most) has different size wheel cylinders front and rear. 1-3/16" front and 1" in the rear. Isn't this the way the pressure is balanced between the front and rear? Todd[/QUOTE]

Wouldnt this statement be the reason no valving is needeed? I also will be making the same change in a ford product so I also need to know.

 

Probably some confusion here - 1966-70 factory drum and factory disc cars have a distribution block which is identical whether the car was drum or disc. Although very similar in appearance to a proportioning valve, the distribution block does not alter brake line pressure. The distribution block keeps front and rear systems separate, splits the left and right front lines and houses the sending unit for the brake failure warning light. Only the disc brakes models got the added feature of Proportioning

 

eci ...call them ,... end of story . they have it

 

huh, well i learned something new today

 

I have 65 Chevy axles on my 29 Ford. I am using a dual M/C and have drum brakes ft and back. No valve and they have been good to go for several yrs. Iceman

 

This is wrong. He said an upgrade to a 60 Belair. The M/C is on the firewall so no residual valve is needed. Only if the M/C is below the calipers or wheel cyliders. The fluid will drain back to the M/C if you don't have one at that point. I know it was mentioned but it's worth mentioning again.

 

Sorry, but drums need a RPV wherever the cylinder is mounted to prevent air being*****ed in past the wheel cylinder seals when the brakes are released. I think that some wheel cylinders have a cup expander thingy behind the seal that does the same job, but not sure how common that is.

 

Funny, but my stock '37 Chevy's drum brakes don't have a RPV, either free standing or in the m/c, nor is there a proportioning valve and they've been stopping pretty damn good for the last 75 years or so..........

 

Per ECI Brakes;
10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if you are not sure whether you have one or not, put one in. They are not****ulative and it won't hurt anything if you have two. Don't worry about brake drag, it takes roughly 75 PSI to overcome the return springs.

 

Wouldnt this statement be the reason no valving is needeed? I also will be making the same change in a ford product so I also need to know.[/QUOTE]

My point EXACTLY!!! Todd

 

Not trying to be an****, but are you sure?

This '37 Chevy service bulletin shows a check valve in the master cylinder.

http://chevy.oldcarmanualproject.com/bulletins/37csn48.htm

 

I think your mistaken, it's with disc brakes you need one if the master is below the leval of the calipers and in that case you use a 2lb residual valve. Drum brakes need a 10lb no matter where the master is.

 

You probably won't need a proportioning valve but it won't hurt to have one in case you find you do need it.

 

I'm running disks on the front, drums on the rear .
the master cylinder is not boosted.
I have been told I DO NOT need aproportioning
valve. Is this correct?
Thanks

 

If nothing else it gives you the opportunity to really dial in the brake bias. Especially if your running a different rear end that may have a little different drum brakes. BUCKD

 

The short answer is, NO. I don't know of any production disc/drum vehicles that does not have a prop valve.
The reason is disc brakes require higher line pressure for a given deceleration than drum brakes, and without a prop valve early rear slide can/will occur during heavy braking.
The odds are you will need one on a custom system, so you're better off installing one, power-assisted or not. This will also help with rear bias adjustment whenever changing pad/shoe lining or tire type/size.